The image recording element used to record images in an electrophotographic printer/copier is often in the form of a cylindrical drum having a photoconductive outer surface. In a well-known manner, transferable visible images are formed on the drum's photoconductive surface by rotating the drum about its central axis so as to advance the photoconductive surface past the various image-processing stations that carry out the electrophotographic process. These stations typically include a corona charging station for uniformly sensitizing the drum surface with electrostatic charges; an exposure station for imagewise exposing the charged surface with actinic radiation to selectively dissipate the uniform charge, leaving behind a latent electrostatic charge image; and a development station for applying electroscopic toner to the charge image to render it visible. The toner image thus formed is then transferred to an image-receiver sheet (e.g., a sheet of plain paper) so that the drum surface can be recycled through the image-forming process to produce multiple copies or prints. Transfer of the toner image can be made either directly to the image-receiver sheet, or indirectly to the image-receiver sheet via an intermediate image-transfer drum, e.g., a plastic-coated drum, to which the toner image is first transferred before being transferred again to the image-receiving sheet. Following image transfer, one or more cleaning stations operate to remove any residual toner from the drum surface(s).
As will be appreciated, the operative outer surfaces of image-recording and image-transfer drums of the above type are relatively delicate in nature. Virtually any scratch, mark, gouge or the like on the drum surface is likely to give rise to an artifact in the toner image formed thereon. Thus, from the time of drum manufacture until the time a drum is eventually installed in its host printer/copier, substantial care must be taken to guard against, or at least minimize, any physical contact with the drum's sensitive outer surface. Typically, image-recording drums are shipped from the manufacturer in a sealed, light-tight container or box in which the drum is supported, e.g., at its edges or by opposing axles, so that its' photoconductive surface is spaced from all surfaces within the container. The container may be fitted with yokes or the like for supporting the drum axles.
To facilitate drum installation while guarding against any deleterious contact with the drum's photoconductive surface, it is common to movably mount most, if not all, of the various image-processing stations of the printer/copier for movement between their operative position and a clearance position. In their respective operative positions, each processing station is either in contact with, or in close proximity to, the path traversed by the drum surface so that the station can act upon the drum surface in carrying out its intended function. In their respective clearance positions, the processing stations are substantially spaced from the drum path, perhaps by as much as 30 mm. This spacing is intended to provide ample room for the drum-installing technician to maneuver or slide the drum axially, e.g., towards and away from its operative position, without making any contact with the internal components of the processing stations. This need for ample spacing can have a significant effect on the overall size of the printer/copier, making it somewhat larger than it theoretically need be. Ideally, the minimum clearance spacing required to install or replace a drum is slightly more than that required to free the drum from physical contact with those processing stations that need to contact the drum surface to carryout their respective functions, e.g., the development, cleaning, and image-transfer stations. But using this minimum spacing in the design of a printer/copier is apt to jeopardize the integrity of the drum surface during drum installation and removal. Moreover, it increases the technician skill level required to effect these operations.
In U.S. Pat. No. 4,823,160 issued to Ikuta et al., apparatus is disclosed for facilitating the loading and unloading of a photosensitive drum in an electrophotographic printer or copier. The design of this loading/unloading apparatus presupposes that the drum comprises a replaceable photosensitive outer sleeve that is supported by an inner cylindrical member mounted on a drive shaft. The cylindrical support member is part of the printer/copier and is not itself replaceable with the photoconductive sleeve. One end of the drive shaft is secured to the rear wall of the printer/copier frame, and the cylindrical support member is slidably mounted on the drive shaft. Thus, to replace the photoconductive surface of the drum, the cylindrical support member is slided along the drive shaft until a major portion of such member clears the front wall of the machine. Thereafter, the photoconductive sleeve is removed by sliding it axially off the free end of the cylindrical support member. While this apparatus may be useful in minimizing the aforementioned clearance space required to install a drum amid the various image-processing stations of an electrophotographic printer/copier, it does not address the problem of minimizing contact with the photoconductive surface by the drum-installing technician. Here, the technician must physically handle the photoconductive sleeve in placing it on the cylindrical support member. Further, as mentioned, the apparatus is useful with a drum assembly in which only the photoconductive sleeve is replaceable, not one in which the entire assembly, including the sleeve-supporting structure, is replaceable.